254 A - RICHARI) s. 



similar to those which led Van der Stricht to conclude that the 

 nuclear sap passes to the poles of the spindle and is equally 

 divided by the ensuing halving of the blastomere. The fibers 

 are apparently grouped into bundles leaving spaces along which 

 the clear streams of nuclear sap may flow to the poles. Van der 

 Stricht regards this as evidence that the sap of the dividing 

 nucleus gives rise to that of the daughter of nuclei. 



In general the events which take place during the metaphase 

 of mitoses in these eggs at least during the earlier cleavage 

 divisions, do not differ greatly from those occurring regularly in 

 the majority of animal and plant cells. It is with those phases 

 of the mitotic cycle that follow the metaphase and continue until 

 the stage of formation of the new metaphase is reached, that are 

 of especial note here. 



Fig. 2 shows the conditions obtaining at the moment of 

 chromosomal division. Three of a group of chromosomes are 

 here half divided and the ends are pulling apart preparatory to 

 their separation in the anaphase. Already it is possible to 

 detect the chromomeres of which the chromosome is composed. 

 The metaphase represents the stage of maximum contraction of 

 the chromosomes. It seems that at the moment of separation 

 the chromosome begins to loosen up. This may be interpreted 

 to mean that their permeability increases at this time; at any 

 rate they take in liquid (water or cell sap?) resulting in the 

 swelling up of chromosomes and consequent separation of the 

 chromomeres. It is in this manner that a chromosomal vesicle 

 begins its formation. As a result of this process the chromosomes 

 lose their property of staining densely, and until they have passed 

 well into the telophase, the walls of the vesicles thus formed 

 retain the chromatic stain longest. As the vesicle grows, how- 

 ever, it is seen that the latter characteristic is really misleading, 

 for the walls are merely lined with very fine granules of chromatin 

 which later become separated by the increasing growth of the 

 vesicle. 



Fig. 3 is an anaphase. The loosening up process here has 

 brought out the true character of the chromosome. A chromo- 

 some consists of two substances, linin and chromatin, of which 

 the former is in the nature of a sheath or sac, while the latter 



